1. Field of the Invention
The present invention relates to a projection display system having a light modulator display device, and more particularly, to a micro-mirror light modulator and projection display system using the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for displaying an image by modulating a luminous intensity of pixels by means of micro-mirrors.
2. Discussion of the Related Art
Generally, projection display systems display a wide image on a wide screen by enlarging and projecting a small image. An example of a conventional projection display system is an LCD (liquid crystal display) projection display system that uses a lamp and LCD display device.
FIG. 1 is a schematic diagram of a conventional LCD projection display system. Referring to FIG. 1, in a basic configuration of an LCD projection display system in the prior art, a light emitted from a lamp 11 is collimated in one direction by a reflector. A red light is transmitted through a red filter 12, whereas green and blue lights are reflected by the red filter 12.
The red light is reflected by a red mirror 13 to be irradiated onto an R-LCD (Red LCD) 17, the green light is reflected by a blue filter 14 to be irradiated onto a G-LCD (Green LCD) 18, and the blue light is transmitted through the blue filter 14. The projected blue light is reflected by a first blue mirror 15 and a second blue mirror 16 to be irradiated onto a B-LCD (Blue-LCD) 19.
Each of the R-, G- and B-LCDs 17, 18 and 19 displays an image for each color in response to an electrical signal in which the corresponding image is encoded. The images of the respective colors are combined by a prism 20. The combined color image is projected to a projection optical system 21 so that the projected image can be viewed on a screen 22.
The LCD display device, which has a relatively slow response speed, exhibits the problem of causing image artifacts when displaying a fast-moving picture. In addition, when the LCD display device operates to render a dark pixel in response to an off value of the electrical signal, the liquid crystal layer of the LCD display device generally is unable to completely block the light of the pixel. This dark state light leakage typically reduces the contrast of LCD projection display systems.
Conventional LCD projection display devices typically include optical systems with color separation and combination systems that increase the complexity and the overall size of the projection display devices.
FIG. 2 is a perspective diagram of a DMD (digital micro-mirror device) according to a related art. Referring to FIG. 2, a DMD is fabricated by covering each memory cell of a CMOS SRAM with a micro-mirror. The DMD is configured to have a pair of micro-mirrors 23 and 23′ for one memory cell. One mirror 23 is rotated by +10° while the other 23′ is rotated by −10°. A binary state of ‘0’ or ‘1’ is represented in each basic memory cell.
In FIG. 2, reference numbers 25, 26, 27, 28, 29, 30 and 31 indicate a yoke landing tip, support post, tension hinge, yoke, mirror landing electrode, yoke address electrode and mirror address electrode, respectively.
The DMD having the above configured memory cells is fabricated by regularly arranging 100,000˜10,000,000 micro-mirrors in width and length directions according to a semiconductor process. By controlling the tilt of each of the mirrors by ±10° according to a voltage applied to each of the mirrors, the intensity of the light reflected by the corresponding mirror is adjusted to implement video information of each pixel.
Namely, an on-state light is reflected in the direction of the projection lens (not shown in the drawing) with a specific angle by the micro-mirrors 23 and 23′ moving in a diagonal direction, whereas an off-state light is reflected with an opposite angle in a direction away from the projection lens. Hence, the DMD can be used as a spatial light modulator.
However, as can be seen in FIG. 2, the configuration of the DMD is complicated and three-dimensional. Hence, the fabrication throughput of the DMD is low, which makes the DMD relatively expensive.
Alternatively, the projection display system may include a GLV (grating light valve), which is a display device employing micro-ribbons. FIG. 3A is a schematic perspective diagram of a GLV. Referring to FIG. 3A, a set of six ribbons 33 and 34 forms one pixel 100. The ribbons 33 and 34 are alternately arranged. In this case, operational ribbons 33 are moved by an electrode 32, whereas fixed ribbons 34 are not moved by the electrode 32. In the above configuration, 100˜10,000 micro-ribbons are arranged by a semiconductor process to form a linear display device, which can be used to render an image on a line of pixels.
FIG. 3B is a diagram of a projection display system employing the above configured GLV. Referring to FIG. 3B, the projection display system includes a first condenser lens 35 for focusing the R, G and B components of the image, a GLV 36 with three rows of pixel elements (i.e., R, G, B), a second condenser lens 37 for focusing the light from the GLV 36, and a scanner 38 for scanning the light from the second condenser lens 37 onto a screen 39.
When a voltage is applied to the above configured projection display system, the operational ribbons 33, to which the voltage is applied, are deflected downward while the fixed ribbons 34 do not move. Thus, this configuration of ribbons forms a grating with a periodic step shape in height. As the R, G and B light components are directed onto the GLV 36 via the first condenser lens 35, the grating diffracts the light.
The light diffracted by the GLV 36 is scanned by the scanner 38 to effectively convert the one-dimensional array of pixels associated with the GLV 36 to an image projected onto the screen 39 as a two-dimensional array of pixels.
In the projection display system employing the GLV, the GLV has a hollow solid shape. However, the deflected operational ribbons 33 contact the substrate over a relatively large area, which often results in sticking of the deflected operational ribbons 33 with the substrate. Moreover, a high voltage is needed to move the relatively wide ribbons.